The present invention relates to redundant power supply systems. In particular, the invention relates to a method and apparatus for testing for faults in the isolation circuits of systems powered by redundant power supplies.
It is customary in redundant power supply systems to provide a number of isolation devices, which serve to isolate inoperative power supplies from any unwanted backflow of current. The inoperative state in one (or more) of the power supplies may be intentional or alternatively may occur due to a malfunction.
Due to the nature of their operation, it is inherently the case that the presence of certain types of faults in isolation devices (such as a short circuit) only become apparent when the power supply which it serves to isolate becomes inoperative. A latent fault in an isolation device may therefore develop while the associated power supply is in the operative state and remain undetected until that power supply becomes inoperative.
However, it is in the inoperative state that each power supply relies upon its associated isolation devices for protection from the backflow of current. Should it remain undetected, the development of a latent fault in an isolation device has potentially disastrous consequences, which may lead to catastrophic failure in its associated power supply or in other power supplies in the system.
Therefore, it is desirable to be able to test the integrity of each isolation device ‘before the event’, while each associated power supply is in the operative state, thereby ensuring the protection of each power supply from unwanted backflow currents in the inoperative state.